From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C748BC433F5 for ; Fri, 7 Oct 2022 15:10:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229981AbiJGPKM (ORCPT ); Fri, 7 Oct 2022 11:10:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229754AbiJGPJy (ORCPT ); Fri, 7 Oct 2022 11:09:54 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED0C114D33 for ; Fri, 7 Oct 2022 08:09:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=IkEJ5cvuj/MJi7gwVwOtxmnQ/38uKGNjLnka1yFw7EI=; b=ZeG9jlVGWcNrymTsjYfOhguAT3 Bz1QK94ec0U/Ipkr33Ge+rN2pXBXN0CHi3/j3V0cnX4pxMJN3k1dVGB2YtndtQCvQSr0VxvdR8n7i wSsmWC0fAwHiLnPXjH1CbwtRR0fofQr/u2h1AKAke3n+wgD/jwKm2RNXZg6NDsiGm/S3RsHzG+AhA EozMgaZRukDhIqU+YjJz3preibby0nNmrEdp19jrbW/JAVQv+fHCa9D4IgBC4/LTKUBEPYAJJ0SlQ oXPTHUzWSnwloh/zDPnEETVXfZe8ShAQUJRs0kLLl2UDVjbc+Ht3Pc/LILEZUDmZ8Gkglhm8Box4o CTbIX2Xw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1ogoyl-001UPZ-Bh; Fri, 07 Oct 2022 15:09:35 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id ACA7F300155; Fri, 7 Oct 2022 17:09:34 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9631629982FD4; Fri, 7 Oct 2022 17:09:34 +0200 (CEST) Date: Fri, 7 Oct 2022 17:09:34 +0200 From: Peter Zijlstra To: Xin Li Cc: linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com Subject: Re: [PATCH 6/6] x86/gsseg: use the LKGS instruction if available for load_gs_index() Message-ID: References: <20221006154041.13001-1-xin3.li@intel.com> <20221006154041.13001-7-xin3.li@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221006154041.13001-7-xin3.li@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 06, 2022 at 08:40:41AM -0700, Xin Li wrote: > static inline void native_load_gs_index(unsigned int selector) > { > + u16 sel = selector; > + > + /* > + * Note: the fixup is used for the LKGS instruction, but > + * it needs to be attached to the primary instruction sequence > + * as it isn't something that gets patched. > + * > + * %rax is provided to the assembly routine as a scratch > + * register. > + */ > + alternative_io("1: call asm_load_gs_index\n" > + ".pushsection \".fixup\",\"ax\"\n" > + "2: xorl %k[sel], %k[sel]\n" > + " jmp 1b\n" > + ".popsection\n" > + _ASM_EXTABLE(1b, 2b), > + _ASM_BYTES(0x3e) LKGS_DI, > + X86_FEATURE_LKGS, > + ASM_OUTPUT2([sel] "+D" (sel), ASM_CALL_CONSTRAINT), > + ASM_NO_INPUT_CLOBBER(_ASM_AX)); > } Something like so perhaps? asm_inline volatile("1:\n" ALTERNATIVE("call asm_load_gs_index\n", LKGS_DI, X86_FEATURE_LKGS) _ASM_EXTABLE_TYPE_REG(1b, 1b, EX_TYPE_ZERO_REG, %k[sel]) : ASM_CALL_CONSTRAINT : [sel] "D" (sel) : "memory", _ASM_AX); (completely untested, not even seen a compiler upclose)